1. Field of the Invention
This invention relates to a device for clamping a movable carriage to a moving drive belt. It is particularly concerned with providing secure clamping to a movable drive belt of a component which is required to make movements involving rapid acceleration and/or retardation
2. Description of the prior art
A specific need for such secure clamping arises in the transverse cutting of a high speed web of photographic material, for example as it emerges for rewinding after passage through a line in which it is coated with photosensitive material. Our European patent application 93 200043.3 filed on Jan. 8, 1993 and entitled "Web cutting device", relates to a cutting device for this purpose wherein a movable cutting head must be securely attached to an endless loop drive belt. The clamp of the present invention is especially well suited to use with the device of the said copending application and is primarily described herein with reference thereto.
A typical automated arrangement for rewinding of a web of photographic material comprises a turret including a rotatable holder for two cores. Winding commences on a first empty core and continues until a full roll has been wound. As the winding approaches the full-roll stage, the holder moves a second empty core towards and close to, but still out of contact with, the path of travel of the web upstream of the filling core. When the latter core is fully wound the web is cut close to the empty core. The new leading edge of the web is brought-into contact with the empty core for attachment thereto, normally with the assistance of a pre-applied adhesive strip on the core surface. The full roll is then removed from the holder and replaced by a new empty core.
The device of our said co-pending patent application comprises a frame with a fixed track, a fixed driving bar and a motor-driven belt, all of which extend across and beyond the path of the web, and further comprises a movable carriage which incorporates a drive wheel rotatable by contact with the fixed driving bar to drive a web-cutting blade. Because most of the components required to drive the cutting blade are accommodated on the frame, the carriage is of simple and lightweight construction such that it can be accelerated from rest to the desired cutting speed within a region of the frame situated beyond one edge of the web, i.e. outside the point at which the blade contacts the web. The blade traverses the web at a fast and uniform cutting speed which ensures the required clean cut and is then retarded to rest after the cut is complete, the retardation being also accomplished within a section of the frame beyond the other edge of the web.
In a typical web turret, however, the available space beyond the width of the web is severely limited and the acceleration and retardation must therefore be accomplished in a short lateral distance, typically in the range 300 to 400 mm. The required acceleration and retardation of the carriage in the available space must therefore be very high, for example up to 15 G. A fixed coupling arrangement, such as a carriage bolted to a driving belt, would suffer from the disadvantage that if for any reason, for example failure of the electronic control circuit or motor defect, the carriage is not decelerated within the available distance, the carriage would strike the machine frame and become damaged or destroyed.